PHOTOLYSIS OF SOME UNSYMMETRICAL PHOSPHINIC AZIDES IN METHANOL. RELATIVE MIGRATORY APTITUDES OF ALKYL GROUPS AND PHENYL IN THE CURTIUS-LIKE REARRANGEMENT.

Article abstract of DOI:10.1016/0040-4020(82)80195-6

When an alkylphenylphosphinic azide RPhP(O)N3 (R=Me, Et, Pr_i or Bu_t) is photolysed in MeOH either the alkyl or phenyl group can migrate from P to N in the Curtius-like rearrangement.The composition of the product shows that migration of the alkyl group R is preferred.However, the preference is not great and decreases as R changes Bu_t->Pr_i->Et->Me-> (approx. migratory aptitudes relative to Ph: 2.1, 1.7, 1.3, 1.2 respectively), probably because the Ph-P bond is better able to assume the correct conformation for Ph migration when R is less bulky.For t-butylmethylphosphinic azide there is very little preference for migration of Bu_t relative to Me.Small amounts of unrearranged products such as Bu_tPhP(O)NHOMe and Bu_tPhP(O)NH2 are generally produced in the photolyses, together with the methyl phosphinates RPhP(O)OMe (major product when R=Me) resulting from (non-photochemical) solvolysis of the azide.